High-resolution millimeter-wave spectroscopy of metal-containing species: Examining fundamental ligand interactions

Abstract

Millimeter-wave spectroscopy has been used in this thesis to accomplish two main goals: (1) to study bonding, structural, and electronic properties of small, metal-bearing molecules in their ground electronic states, in particular how individual metal atoms bond to small ligands, and (2) to provide rest frequencies for radio astronomical searches of metal containing species in the interstellar medium. The types of molecules studied in this thesis can be broadly classified into three groups: (1) alkali and alkaline-earth amides (MNH₂), (2) diatomic molecules in high electron spin or high orbital angular momentum electronic ground states (MX), and (3) transition metal cyanides (MCN). In this first category, the pure rotational spectra of LiNH₂ (X¹A₁), LiND₂ (X¹A₁), NaND₂ (X¹A₁), MgNH₂ (X²A₁), and MgND₂ (X²A₁), were recorded and analyzed. For each, the first experimental monomer r₀ structures were determined. These species were found to be planar and not invert, in contrast to ammonia. In addition, for the alkaline-earth amides, the M-N bond appears to become less ionic from Sr to Ca to Mg. The second class of molecules investigated, high-spin diatomcs, includes: NaC(X⁴Σ⁻), CrN(X⁴Σ⁻), CrO(X⁵Πᵣ), MnF(X⁷Σ⁺), FeN(X²Δᵢ), FeC(X³Δᵢ), and TiF(X⁴Φᵣ). These species represent examples of electronic states that have never or seldom been observed by high-resolution millimeter-wave spectroscopy, due to their high values of electron spin and orbital angular momenta. The analysis of their spectra has been used to test the adequacy of the effective Hamiltonians developed to model their rotational spectra; in particular the use of theoretically predicted higher order parameters. The final group studied includes the transition metal cyanides CoCN (X3Φᵢ ) and NiCN (X2Δᵢ). Unlike their alkali, alkaline-earth, and group 13 counterparts, these species were determined to be linear cyanides with the metal atom bonded to carbon, similar to both CuCN (X1Σ⁺) and ZnCN (X2Σ⁺). For both molecules, complications in the rotational spectra due to the Renner-Teller effect were observed and analyzed.